When crushing or grinding rock, ore, cement clinker and other hard materials roller crushers may be used having two generally parallel rolls which rotate in opposite directions, towards each other, and which are separated by a gap. The material to be crushed is fed by gravity or choke-fed into the gap. One type of roller crusher is called high pressure grinding rollers or high pressure roller crushers. This type of roller crusher uses a crushing technique called interparticle crushing. Here, the material to be crushed or pulverised is crushed not only by the crushing surface of the rolls, but also by particles in the material to be crushed, hence the name interparticle crushing.
One example of a high pressure grinding roller is described in EP-516 952. The document discloses an improved roll for a roller press capable of withstanding very high nip forces in a press nip for interparticle crushing. The roller press has a plurality of spaced wear-resistant surface members embedded in the pressing surface of the roll which are of a material harder than the material of the roll surface surrounding the inserts. By varying the size and number and material properties of the embedded pieces, the wear of the press roll is matched to the materials to be comminuted to minimize wear and to match the wear profile along the roll with extended pressing use.
A general problem associated with existing high pressure grinding rollers is that the ratio between the roller diameter and the roller width is very important due to a significant edge effect, i.e. the crushing result is reduced at the edges of the rollers. This is because of the fact that material can escape over the edges of the rollers thereby reducing the crushing pressure on the over the edges of the rollers thereby reducing the crushing pressure on the material towards the gap at the edges of the rollers. Thus, these roller parameters cannot be varied to the desired extent.